Memory provides data storage for electronic systems. Flash memory is one type of memory, and has numerous uses in computers and other devices. For instance, personal computers may have BIOS stored on a flash memory chip. As another example, flash memory is used in solid state drives to replace spinning hard drives. As yet another example, flash memory is used in wireless electronic devices as it enables manufacturers to support new communication protocols as they become standardized, and to provide the ability to remotely upgrade the devices for improved or enhanced features.
A typical flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. The flash memory may be erased and reprogrammed in blocks. NAND may be a basic architecture of flash memory. A NAND cell unit comprises at least one selecting device coupled in series to a serial combination of memory cells (with the serial combination commonly being referred to as a NAND string). Example NAND architecture is described in U.S. Pat. No. 7,898,850.
Memory cell strings may be arranged to extend horizontally or vertically. Vertical memory cell strings reduce horizontal area of a substrate occupied by the memory cells in comparison to horizontally extending memory cell strings, albeit typically at the expense of increased vertical thickness. Vertical memory cell strings are usually fabricated in multiple stacks or decks which facilitates the manufacturing thereof. Each stack includes vertically-alternating tiers comprising control gate material of individual charge storage transistors that vertically alternate with insulating material. A channel pillar extends through each of the stacks and a conductive interconnect electrically couples the channels of immediately elevationally adjacent channel pillars together. Conductively-doped polysilicon is one example material for the conductive interconnect. Such may, for example, be conductively doped with phosphorus (an n-type material). The phosphorus can diffuse elevationally above and below the polysilicon into the upper and lower stack channel materials. More may diffuse down than up which can adversely impact programmable memory cells in the elevationally outermost portion of the lower stack.